Object Update

Requirements

• Export updateObject(input, path, updater) as named and default. path is an array of string object keys or numeric array indexes. Call updater once with the current own value at the path, or undefined when missing, and insert its return value.
• An empty path updates the root itself. Preserve the original root and ancestors when the updated value is Object.is-equal to its previous value. Returning undefined for a missing path is also a no-op and does not create containers.
• Create missing containers based on the next path segment: numeric segments imply arrays; string segments imply ordinary objects. Replace primitive/non-plain intermediates when a deeper path needs a container.
• Clone only changed ancestors. Preserve references to untouched branches, object/null prototypes, array length and holes, and existing own enumerable string properties. Inputs are acyclic data trees; symbols, descriptors, getters, and array extra properties are outside scope.
• Numeric indexes must be integers from 0 to 4294967294. Existing arrays require numeric path segments. Reject invalid segments or __proto__, constructor, and prototype segments with TypeError. Validate forbidden segments before invoking updater.
• Do not mutate or delete input properties. An updater returning undefined for an existing non-undefined value assigns undefined rather than deleting the key. Updater must be pure; deep cloning, dotted string path parsing, and automatic merging are outside scope.

Examples

Input: updateObject({ user: { score: 1 }, active: true }, ["user", "score"], value => value + 1);
Output: { user: { score: 2 }, active: true }, with new user/root objects.

Input: updateObject({}, ["items", 2, "name"], () => "Ada");
Output: Creates items as a sparse array with { name: "Ada" } at index 2.